Is SIP trunking worth the jump?

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Sep 21st, 2009
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So, is SIP trunking really worth the jump? I've been approached by at least 2 ITSPs about making the jump from my PRI to SIP trunk. They promised low cost, fast ROI, reliability, scalability...all the puzz words. My questions to the expert in this forum; is SIP really worth it?

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virverma Mon, 09/21/2009 - 17:11
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thats true,

but few things you need to know....

As is often the case with emerging technologies, some facts about SIP are overlooked and some of its capabilities are overstated. By itself, SIP is not a communications panacea-it works with many other standards to foster open, reliable, rich multimedia communications.

Important facts about SIP:

>> SIP is a signaling protocol that is independent of transport protocol; it can run on top of several transport protocols, including User Datagram Protocol (UDP), TCP, and Stream Control Transmission Protocol (SCTP).

>> SIP does not mandate or include specific quality of service (QoS) capabilities; it works with other protocols that perform this function.

>> SIP is independent of any security protocol and may be used with several security protocols, such as Transport Layer Security (TLS) and IP Security (IPSec).

>> SIP is a peer-to-peer protocol, not an IP-to-PSTN gateway control protocol such as MGCP or H.248.

>> SIP provides methods to control sessions, but does not specify the applications and services that will use those sessions; as a result, SIP does not guarantee application behavior.

>> SIP is independent of the media used, allowing the flexibility to initiate sessions for different media types.

KonradStepniewski Mon, 09/21/2009 - 23:43
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I would say yes and no. PRI is very stable and you don't have much problems after installation. SIP is still under development and not as stable.

I use both in my company, PRI for major sites and SIP for branch offices. No big plans to go SIP everywhere.

paolo bevilacqua Tue, 09/22/2009 - 00:47
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SIP is still under development and not as stable

That's not quite correct. Even if SIP is under development, that is not what is causing instability. There are no instabilities in the protocol itself or in a regular connection after proper initial configuration.

The point is that you're connecting over the Internet and that is intrinsically less reliable than a PRI circuit and a CO switch.

Oh, and ask about the ITSP how do they support fax. Some just don't.

If they can port your current number to SIP.

How they provide billing.

There are a lot of aspects to consider beside cost.

Nicholas Matthews Tue, 09/22/2009 - 04:19
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A lot of the inconsistency with running SIP over the internet is to couple your ISP and your SIP provider. When they are the same company, there isn't a fight as to who is creating the voice quality problems. These can be pretty easy to determine with packet captures.

Example: You're getting static on your calls. On a PRI, you've got to go through a huge rigamarole to get a capture on the TDM to get a PCM capture. Even then, there will still be argument over who may be causing it. In an IP environment, you get a packet capture in the middle, and it will tell you.

There are some things that are simpler with SIP, and some that are not. Fax is not. Portability and flexibility are simpler. As well as saving money on cost, you can also get rid of a good portion of your DSPs since those are no longer necessary.

PRIs are already disappearing very quickly, and SIP is becoming a solution for a lot of people.


bradyk0uc Mon, 09/28/2009 - 13:31
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Another thing to consider is security. It's another IP path into your network (possibly). Not too many security issues on PRIs. :)

You may have to firewall the SIP connection if it's a new IP connection to your network.


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